The present invention relates to a spacer arrangement and more particularly to such arrangements used in gas turbine engines in such situations as to accommodate for thermal variations, etc between such components as between an engine casing and unison ring.
Operation of gas turbine engines is well known. Essentially, a number of compressor blade assemblies are associated with a number of turbine blade assemblies such that air is compressed by the compressor assemblies into a combustor where fuel and that compressed air are combusted in order to expel a thrust gas flow through the turbine which in turn thereby drives the compressor assemblies as well as provide thrust in an aircraft or shaft rotation in stationery engines. Clearly, in such arrangements, appropriate control and manipulation of gas flows is important. Similarly, account must be taken of the variations in engine dimensions due to thermal expansion and deformations. For example, it is relatively common for a gas turbine engine to incorporate variable vanes for utilisation between different compressor blade stages and/or turbine blade stages in order that the gas flow is orientated correctly for a subsequent compressor blade stage, or turbine blade stage, for efficient or higher performance operation. These variable vanes are typically adjusted utilising a so called unison ring assembled on the periphery of the gas turbine engine around that engine's casing. In any event, accuracy and reproducibility of operation is required, so means for suppressing variations of the compressor casing, or turbine casing, and/or unison ring growth are beneficial.
Previously, such casing and unison ring growth suppression has been achieved by a spacer arrangement comprising a resilient element to provide balanced compression between the casing and unison ring for retention of position. More recently as shown in U.K. patent application no. 0326544.4, bowed bi-metal strips have been used to alter the compression force in response to temperature. However, such strips may not be able to provide sufficient compression force over the full range of potential variation in gap between the casing and unison ring.